Enantioselective Cyclopropanation of a Wide Variety of Olefins Catalyzed by Ru(II)-Pheox Complexes

Beyond Iron: Iridium-Containing P450 Enzymes for Selective Cyclopropanations of Structurally Diverse Alkenes

Enzymes catalyze organic transformations with exquisite levels of selectivity, including chemoselectivity, stereoselectivity, and substrate selectivity, but the types of reactions catalyzed by enzymes are more limited than those of chemical catalysts. Thus, the convergence of chemical catalysis and biocatalysis can enable enzymatic systems to catalyze abiological reactions with high selectivity. Recently, we disclosed artificial enzymes constructed from the apo form of heme proteins and iridium porphyrins that catalyze the insertion of carbenes into a C-H bond. We postulated that the same type of Ir(Me)-PIX enzymes could catalyze the cyclopropanation of a broad range of alkenes with control of multiple modes of selectivity. Here, we report the evolution of artificial enzymes that are highly active and highly stereoselective for the addition of carbenes to a wide range of alkenes. These enzymes catalyze the cyclopropanation of terminal and internal, activated and unactivated, electron-rich and electron-deficient, conjugated and nonconjugated alkenes. In particular, Ir(Me)-PIX enzymes derived from CYP119 catalyze highly enantio- and diastereoselective cyclopropanations of styrene with ±98% ee, >70:1 dr, >75% yield, and ∼10,000 turnovers (TON), as well as 1,2-disubstituted styrenes with up to 99% ee, 35:1 dr, and 54% yield. Moreover, Ir(Me)-PIX enzymes catalyze cyclopropanation of internal, unactivated alkenes with up to 99% stereoselectivity, 76% yield, and 1300 TON. They also catalyze cyclopropanation of natural products with diastereoselectivities that are complementary to those attained with standard transition metal catalysts. Finally, Ir(Me)-PIX P450 variants react with substrate selectivity that is reminiscent of natural enzymes; they react preferentially with less reactive internal alkenes in the presence of more reactive terminal alkenes. Together, the studies reveal the suitability of Ir-containing P450s to combine the broad reactivity and substrate scope of transition metal catalysts with the exquisite selectivity of enzymes, generating catalysts that enable reactions to occur with levels and modes of activity and selectivity previously unattainable with natural enzymes or transition metal complexes alone.

Diastereoselective Synthesis of Spirocyclopropanes under Mild Conditions via Formal [2 + 1] Cycloadditions Using 2,3-Dioxo-4-benzylidene-pyrrolidines

A highly diastereoselective cyclopropanation of cyclic enones with sulfur ylides was developed under catalyst-free conditions, producing multifunctional spirocyclopropanes in generally excellent yields (up to 99% yield and >99:1 d.r.). The asymmetric version of this method was realized by using an easily available chiral sulfur ylide, affording products with moderate to good stereoselectivity.

Ru(ii)-Pheox-catalyzed Si–H insertion reaction: construction of enantioenriched carbon and silicon centers

We established a highly enantioselective Si–H insertion reaction to construct chiral centers at the carbon and silicon atoms, using a Ru(ii)–Pheox catalyst.

Highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by Ru(ii)–Pheox complexes

A highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by chiral Ru(ii)–Pheox complexes was developed to give chiral cyclopropyl sulfones in high yields (up to 99%) with excellent trans-selectivity and enantioselectivity (up to 98% ee).

Synthesis of 3-azabicyclo[3.1.0]hexane derivatives via palladium-catalyzed cyclopropanation of maleimides with N-tosylhydrazones: practical and facile access to CP-866,087

The cylcopropanation of maleimides and N-tosylhydrazones is developed, providing a practical route to the mu opioid receptor antagonist CP-866,087.